Project Summary/Abstract Twenty years ago effective treatments for HIV became available, and the lifespan of HIV-infected adults in high-resource settings has increased to within a decade of uninfected individuals. However, if therapy is stopped virus generally rebounds in the blood to pretreatment levels, due to viruses that persist and reactivate from the ?HIV Reservoir?. Curative therapies suitable for the millions of infected individuals have been sought, including strategies using therapeutic vaccines, chemotherapies paired with stem-cell transplant, chimeric antigen receptor cells, gene therapies, cytokines and antiretroviral therapy during acute infection. While many of these have reduced the HIV reservoir and in one case may have cured HIV infection, a better understanding of the mechanisms that allow persistence of the reservoir are needed to develop an effective, safe and economical cure. The HIV reservoir of perinatally infected children are primarily established early in infection when their immune system is tolerogenic to foster a healthy gestation, postnatal colonization with commensal bacteria and tolerance of foods. We propose to examine four mechanisms that could contribute to sustaining the HIV reservoirs and compare the contribution of each in children versus adults. We hypothesize that two mechanisms will be specific to children: (1) immune tolerance of HIV, due to ?perinatal? infection (in utero or the early weeks of life) when immune tolerance to non-self antigens including non-inherited maternal antigens (NIMA) and oral tolerance to foods are established; and (2) ?cross immune tolerance? to HIV generated by increased levels of maternal microchimerism (MMc), as observed with allografts.15 In both adults and children, we hypothesize that the HIV reservoir is maintained by (3) modulation of gene expression by HIV integration in genes of Treg that promote survival of these cells, and/or through impairment of antiviral functions towards other infected cells; and (4) by the persistent loss of gut T-helper (Th)17 cells due to bacterial translocation eliciting pro-inflammatory cytokines that favor the development and persistence of Tregs instead of effective antiviral CD4+ T-cell help. Through studies of specimens collected prospectively from South African children known to have acquired HIV perinatally, their mothers and uninfected controls, we will measure parameters of each of these mechanisms to gain insight into the roles of these mechanisms in sustaining the infectious HIV reservoir. The knowledge gained regarding the relative contribution of these four mechanisms in children vs. adults should point to mechanisms most relevant to children that we could test in non-human primates (NHP), with the goal of developing interventions tailored to the unique mechanisms identified in children.